From forest to ocean, the animal din of grunts, squawks, squeaks and squeals may be the product of complex vocal systems that are only an evolutionary step away from generating humanlike language.

The vocalizations of orangutans, finches, killer whales and four other animal species have some form of grammar and may be more language-like in structure than previously thought, researchers report August 20 in Proceedings of the Royal Society B. The results, along with other studies, challenge the breadth of the disparity between human language and and the seemingly simple generation of sounds animals are thought to produce. More research may reveal an evolutionary step that links the two.